About the noise value of the cooling fan

When our customers get the specifications provided by the cooling fan manufacturer, they will generally indicate the noise value. How should we understand this value? First of all, the noise marked on the data sheet refers to wind noise, not friction noise. It is abnormal sound. Wind noise is necessary for every cooling fan to operate. Secondly, the noise data is whether every fan must be fully inspected. Of course No, the noise of the test fan is tested in a silent room, and it is tested on a computer. The time to test one unit is about 5-10 minutes. The cost of a silent room is about 600,000 yuan. If it is fully inspected, The cost is very high. In addition, because the shape of the fan is fixed, each rotation speed corresponds to a wind noise, and the wind noise increases correspondingly when the rotation speed is high. Therefore, it is not necessary to test each wind noise cooling fan manufacturer. Every fan will be tested for abnormal sound, because abnormality is one of the factors that determine the life of the cooling fan